On Thu, 14 May 2009 12:01:44 +0100
Ian Campbell <ian.campbell@xxxxxxxxxx> wrote:
> I recently noticed that my bridges were flooding traffic for a period of time
> after a topology change. These bridges are part of a Xen host and therefore
> have spanning tree disabled and forward_delay of zero. In this situation there
> is no reason not to begin relearning immediately after a topology change.
>
> The existing code uses hold_time == 0 to suppress learning in br_fdb_update.
> hold_time() returns forward_delay if a topology change has recently occurred
> and ageing_time if not. Setting each of those to zero has slightly different
> semantics: Setting forward_delay to zero effectively means forward immediately
> while setting ageing_time to zero effectively means do not learn.
>
> The solution is to not learn after a topology change only if forward_delay is
> non-zero but to retain the existing behaviour based on ageing_time if a
> topology change has not occured.
Unless STP is enabled, br_topology_change is bogus. It looks like,
the following would avoid the problem?
--- a/net/bridge/br_stp.c 2009-05-14 08:33:01.795909321 -0700
+++ b/net/bridge/br_stp.c 2009-05-14 08:34:32.839883992 -0700
@@ -375,7 +375,8 @@ static void br_make_forwarding(struct ne
if (br->forward_delay == 0) {
p->state = BR_STATE_FORWARDING;
- br_topology_change_detection(br);
+ if (p->br->stp_enable == BR_KERNEL_STP)
+ br_topology_change_detection(br);
del_timer(&p->forward_delay_timer);
}
else if (p->br->stp_enabled == BR_KERNEL_STP)
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